1. Field of the Invention
The present invention relates to injection molding machines and, more particularly, to an injection molding machine with a device which is adapted for the program-controlled exchange of injection molding dies and for the continuous preconditioning of an injection molding die, prior to and during its insertion into the die closing unit of the machine.
2. Description of the Prior Art
The changeover of an injection molding machine from the production of one part to the production of another part requires an exchange of injection molding dies in the die closing unit and, in some cases, also an exchange of injection units.
The exchange of injection molding dies tends to cost a considerable amount of time machine downtime, not only for the detachment and removal of the previously used die assembly and the insertion and attachment of the new die assembly, but also for the transfer from the former to the latter of the various fluid lines for temperature conditioning, including all electrical and other operating connections.
Before production operations can be resumed, the newly installed injection molding die also needs to be preheated to the required operating temperature, as part of the overall die preconditioning procedure. In some cases, it may be sufficient to limit the preheating to the achievement of a given average temperature of the die assembly. In other cases, however, it becomes necessary to establish a preheating temperature gradient as close as possible to the temperature gradient which establishes itself in the die assembly during the production run. For, only with such careful preconditioning will it be possible to hold the maximum weight spread among the parts of an entire production run within the expected range of 0.6 to 0.8% for precision-molded parts. Some injection molding dies may thus require up to two hours and more of preconditioning time.
As part of a mechanized die exchange procedure, it has therefore already been suggested to use hydraulically operated clamping devices in the place of the conventional threaded fasteners to clamp the two die halves to their die carrier plates. Several such clamping devices are known from the prior art. An improved attachment mechanism for interchangeable injection molding dies is disclosed in my copending U.S. patent application, Ser. No. 449,550, filed December 13, 1982, now U.S. Pat. No. 4,473,346.
In a pamphlet entitled "Battenfeld-Symposium mit Sonderschau 4.-7. Mai 1982", it is further suggested to provide a horizontal transfer device in the form of a dolly, the wheels of which are supported on the factory floor. The dolly is guided for longitudinal translational movements along the machine base, carrying on its top a horizontal roller conveyor. A die assembly resting on this roller conveyor can be pushed horizontally into the clamping space of the die closing unit, using a drive spindle, for example.
The two die halves of the die assembly are provided with special back plates which are larger than the die plates themselves, so as to allow for a mechanized insertion and clamping of the die assembly. In the prior art device mentioned, the back plates of the two die halves form upwardly and downwardly protruding flanges with a tapered shoulder profile. The latter is engageable by a plurality of matchingly tapered clamping plungers advancing vertically from above and below against the back plates.
This prior art disclosure further suggests the arrangement of fluid line couplings in the die closing unit which, in the course of insertion or removal of the die assembly, are connected or disconnected, respectively. These line couplings are located on the opposite side of the die exchange dolly, i.e. on the front side of the machine.
Such a device has several shortcomings: Among them are the fact that the movable die carrier plate needs to be moved away from the die and that, consequently, it cannot participate in the support and guidance of the die assembly during the transfer movement. The support of the assembly is therefore one-sided. The problem-free reengagement of the movable die carrier plate over the centering collar of the movable die plate is not assured.
The absence of a positively controlled transfer drive, combined with the fact that the level of the roller conveyor is determined by the engagement between the dolly wheels and the floor, independently of the machine base, preclude a programmed, fully automated exchange of injection molding dies. Furthermore, the fact that the die assembly is guided on only one of the two die carrier plates limits the application of this device to die assemblies of moderate weight.
No provision is made in this prior art device for the possibility of preconditioning a second die assembly, while the first die assembly is still in service in the previous production run.
In the German Offenlegungsschrift (Publ. Application) No. 16 29 746 is disclosed an injection molding machine for rubber articles which makes use of a mold preheating cabinet with a number of preheating compartments into which injection molding dies are deposited, before being transferred onto a rotating platform holding a number of identical die assemblies. Each compartment of the preheating cabinet has a heatable compartment bottom.
The die assemblies are transferred between the preheating cabinet and the rotating platform of the injection molding machine by means of a horizontal conveyor table which can be raised and lowered in a gimbal frame which is rotatable about a vertical axis. The heat input to the die assemblies takes place by exterior convective contact only, and heat input during the transfer of a die assembly from the preheating cabinet to the injection molding machine is not possible.